Power Macintosh DOS Card: Video Sync For LCD Panels

We took measurements using a digital scope with automated time and frequency calculation. The Power Macintosh DOS Compatibility Card produces timing signals which drive Apple monitors, and includes flexibility to work with non-Apple multiple scan monitors. In some of the Power Macintosh DOS Compatibility Card video modes there are slight timing differences between Macintosh and Windows. This is usually not a problem because most monitors can work within specific timing variances. In other words, if the frequencies are off by a small amount, monitors can still synchronize and provide a stable image.

General Suggestions and Background

If possible, test the LCD panel at various video scan rates. When using an LCD panel with the Power Macintosh 6100/66 DOS Compatible computer, test the panel with both the manufacturer provided adapter and no adapter (direct). Using an Enhance video adapter with a multiple scan display lets you test more configurations and frequencies. You may have to adjust the LCD controls (horizontal and vertical position, sync polarity, and so on) to center the image, remove tearing, or properly synchronize the LCD image. Using an Apple 14-inch display or setting the Enhance video adaptor to "J" is the recommended video timing for Macintosh, DOS, or Windows when connecting to an LCD panel.

The following describes the video signaling for different display connections:

* Apple 14-inch display (640x480)
Video modes for Macintosh, DOS, and Windows will be similar but not exactly the same (horizontal = 35 kHz, vertical = 67 Hz).

* Apple 16-inch display (832x624)

Video modes for Macintosh, DOS, and Windows will be similar but not exactly the same (horizontal = 49.75 kHz, vertical = 74.5 Hz).

* VGA (using Enhance video adapter "G")
Video modes for Macintosh and Windows will be similar, but not exactly the same (horizontal = 31.45 kHz, vertical = 60 Hz). DOS will operate at its normal video rate (horizontal = 31.75 kHz, vertical = 71 Hz).